You can't have the parent assembly as Owner and the child part as Image at the same time, because that would result in the WTPart structured inside itself (i.e. an infinitely deep structure).
The root of your issue is caused by the way Windchill builds visualisations - it looks at the WTPart structure, and displays the default representation of each WTPart, the default representation of your top level WTPart is an assembly which doesn't have any geometry itself (it just has a few planes and coordinate systems) so the child part within it doesn't appear.
I'm aware of a few ways of fixing this, there may be others...
- Create a WTPart for the child .prt - Not really practical, especially if there are multiple child .prt files.
- Set the top level WTPart to be a CAD Represented Part - This changes the behaviour of how Windchill builds the visualisation, instead of looking at the WTPart structure, it looks at the CAD structure. This usually fixes the issue, but has a couple of downsides, including breaking the ability to highlight subcomponents in the visualisation pane when selecting it in the tree, and it also creates a static visualisation that doesn't change as the lower level parts change, plus it requires some system configuration to set up.
- Set the assembly to publish as full geometry rather than a positioning assembly - By default, assemblies usually publish as a 'positioning assembly', which means they don't contain the geometry of lower level parts/assemblies, this behaviour can be changed to be 'full geometry' publishing so it outputs the lower level geometry into the PVZ, but this requires some system configuration, and it's a bit clunky, as you generally have to tell the system on a case by case basis which assemblies to publish as full geometry by changing a parameter in Creo.
- Set the part to be inseperable - This is my preferred option, visualisation of child parts just work, plus there's a load of other advantages like not having to manage the .prt in Windchill. The only downside I'm aware of is that it could use more disk space and take more publishing resource
- Change the default representation to be the .prt - I've not tested this, but I think if the .prt is associated as Content, you should be able to change it to be the default representation in the Representations/Annotations table. Probably not very robust, as it could snap back to the .asm being the default representation the next time it's checked in.
- Never associate the .prt to the WTPart - One behaviour I've observed is that if a child CAD part has never been associated to a WTPart, Windchill will show it in the visualisation. This isn't particularly practical though, as you can permanently break the visualisation by accidentally associating it to a WTPart.
Hope that helps.
Graham